1. Field of the Invention
The present invention relates to devices and techniques for generating thermal (heat) energy and electrical energy and, more particularly, to devices and methods adapted to provide heat and electricity to buildings and the like in association with heat and electricity normally provided by public utilities. Specifically, the present invention relates to an improved cogeneration device for providing both thermal and electrical energy to a facility and the like and having substantially improved efficiencies and economics of operation as well as providing maximum electrical energy during times of utility power outages to the facility.
2. Description of the Prior Art
Devices designed to generate both heat and electricity are well known in the art. Some examples of such devices are disclosed in U.S. Pat. Nos. 1,552,661; 1,761,849; 2,051,240; and 4,164,660. In these particular patents, cogeneration units are disclosed having a central power plant that generally consists of an internal combustion engine powered by diesel or other types of fuel. Waste heat from the central power plant is utilized to heat water for thermal heating purposes, and the power output of the plant is designed to run a generator to generate electricity. U.S. Pat. No. 2,130,606 shows a similar type of system which is specifically adapted to heat or cool a residence while simultaneously producing electricity for the residence.
Thermal energy is derived from coolant fluid flowing through the central power unit and drawing heat therefrom as well as from the hot exhaust gases generated by the central power unit. U.S. Pat. Nos. 4,065,055 and 4,264,826 both disclose cogeneration systems which utilize engine exhaust gases for heating and cooling purposes. Finally, U.S. Pat. No. 2,637,305 discloses a similar type of cogeneration system whereby the coolant fluid is first passed through the engine to take up heat and is further heated by the hot exhaust gases from the engine in a heat exchange system. The heat retained by the coolant fluid is then utilized for heating purposes.
One aspect that is in common to all of the above identified prior art cogeneration systems is that the internal combustion engine or other unit utilized as a power source to run an electrical generator must be operated at a speed which provides a constant speed output. Thus, the constant-speed constraint of a conventional generator set requires that the power unit, i.e., generally an internal combustion engine, also be run at a constant speed. This is highly inefficient since the output of the engine is then limited to a fraction of its total capability, and the efficiency of the unit generally drops dramatically when the engine is operated at reduced load. Moreover, the inability to vary the engine's speed in response to varying thermal loads without changing the output frequency of the generator and thus the electrical output is a severe handicap in all the aforementioned prior art systems.